Communication cables have evolved continuously over the years as we have evolved from a voice-based telecommunication network environment to the new structured cabling designs for high-speed data transmission which are commonly referred to as Local Area Networks or LAN's. Technical requirements, standards and guidelines of the Telecommunication Industry Association and Electronic Industry Association (TIA/EIA) and International Standard Organization (ISO) have been developed and published to support high-speed data communication of voice, internet and video. In addition, these requirements continue to evolve with more and more stringent electrical performance needs such that cellular foam insulation and fillers play an increasing role in the cable designs. The primary communications cable designs incorporate twisted copper pairs together to form a balanced transmission line, coaxial cables, and fiber optic cables. All of these cables may be run in a network of a building (LAN's) as separate functional cables or in hybrid or combination cable design.
Furthermore, TIA/EIA has defined standards that are published and recognized as well as industry drafts of soon-to-be published standards for commercial building telecommunication networks. Table 1, which follows, provides those published and pending, or soon-to-be adopted and published Technical Service Bulletin “TSB” standards.
TABLE 1TIA/EIA StandardsCategory 5eFrequencyANSI/TIA/EIA-568-AISO Class DBandwidthCommercial Building Telecommunications Standard Part 2:1 to 100 mhzBalanced Twisted Pair Cabling Component; 2001Category 6FrequencyANSI/TIA/EIA-568-B.2-1ISO Class EBandwidthCommercial Building Telecommunications Standard Part 2:1 to 250 mhzAddendum 1: Transmission Specification for 4 pair 100 ohmCategory 6 Cabling; 2002Category 6AFrequencyANSI/TIA/EIA-568-B.2-10ISO Class EABandwidthCommercial Building Telecommunications Standard Part 2:1 to 500 mhzAddendum 10: Transmission Specification for 4 Pair 100 ohmAugmented Category 6 Cabling; TSB pending publicationCategory 7FrequencyTIA not actively developing standard;ISO Class FBandwidthISO/EIA-11801, 2nd Ed. Information Technology - Generic1 to 600 mhzCabling for Customer Premises, 2002
Each of the standards of Table 1 illustrates continued widened bandwidth enabling greater data transmission. The broadening of communication cable bandwidth enhances the electrical characteristics or data bit rate based on the evolving needs of software, hardware and video transmission. The terminology within the standards for testing can be defined as electrical performance within the cable as measured by impedance, near end and far end crosstalk (NEXT & FEXT), attenuation to crosstalk ratio (ACR), ELFEXT, ELNEXT, Power Sum, etc., and the electrical performance that may be transferred to the adjacent cable a.k.a. (alien cross talk) which are measured within similar performance parameters while incorporating a power sum alien cross talk requirement.
Electromagnetic noise that can occur in a cable that runs alongside one or more cables carrying data signals can create alien crosstalk. The term “alien” arises from the fact that this form of G crosstalk occurs between different cables in a group or bundle, rather than between individual wires or circuits within a single cable. Alien Crosstalk can be particularly troublesome because of its effect on adjacent 4 pair cables which degrades the performance of a communications system by reducing the signal-to-noise ratio. Traditionally, alien crosstalk has been minimized or eliminated by aluminum Mylar® shields and/or braid in shielded cable designs i.e. (Category 7 or ISO Class F shielded designs) to prevent electromagnetic fields from ingress or egress from the cable or cables. The use of foamed or blown constructions for symmetrical and asymmetrical airspace designs further improve electrical performance characteristics in that the overall modulus and elasticity of the resulting foamed compounds are reduced leading to final conformations that more closely approach optimal geometries. Specifically, the ability to form inner structures of cables such that these inner structures have little or no plastic memory once the cabling process is completed, ensures that the nested pairs remain in the desired geometric configuration and that the use of foamed fillers, insulations and jackets using air as an insulator act to mitigate alien crosstalk in Unshielded Twisted Pair (UTP) designs i.e. (Category 6 or ISO Class E and Category 6 Augmented or ISO Class EA).
These Electrical Performance Standards especially for UTP cables (Category 5e, 6, 6A and 7) necessitate improved insulative performance wherein foamed fluoropolymers optimize their inherently excellent insulative values i.e. (dielectric constant and dissipation factor.) Foamed fluoropolymers (such as perfluoropolymers) offer lower cost and lower material content while improving fire retardancy performance by lowering the amount of combustible material in a cable and the overall fire load of Local Area Network cables within a building.
A brief review of the Fire Performance Requirements both in North America and Globally follows:
In 1975, the National Fire Protection Agency (NFPA) recognized the potential flame and smoke hazards created by burning cables in plenum areas, and adopted within the United States, the National Electric Code (NEC), and a standard for flame retardant and smoke suppressant cables. This standard, commonly referred to as “the Plenum Cable Standard”, was later adopted for North America Communications Cabling by Canada and Mexico. The standard permits the use of power-limited type cables that includes communication cables without conduit, so long as the cable exhibits low smoke and flame retardant characteristics. The test method for measuring these characteristics is commonly referred to as the Steiner Tunnel Test. The Steiner Tunnel Test has been adapted for the burning of cables according to the following test protocols: NFPA 262, Underwriters Laboratories (U.L.) 910, or Canadian Standards Association (CSA) FT-6. The test conditions for each of the U.L. 910 Steiner Tunnel Test, CSA FT-6, and NFPA 262 are as follows: a 300,000 BTU/hour flame is applied for 20 minutes to a calculated number of cable lengths based on their diameter that fills a horizontal tray approximately 25 feet long with an enclosed tunnel. This test simulates the horizontal areas (ceilings) in buildings wherein these cables are run.
The criteria for passing the Steiner Tunnel Test UL 910/NFPA 262 are as follows:                A. Flame spread—a maximum flame spread of less that 5.0 feet.        B. Smoke generation:                    1. A maximum optical density of smoke less than 0.5.            2. An average optical density of smoke less than 0.15.                        
The premise of the standard is based on the concerns that flame and smoke could travel along the extent of a building plenum area if the electrical conductors and cable were involved and were not flame and smoke resistant. The National Fire Protection Association (“NFPA”) developed the standard to reduce the amount of flammable material incorporated into insulated electrical conductors and jacketed cables. Reducing the amount of flammable material would, according to the NFPA, diminish the potential of the insulating and jacket materials from spreading flames and evolving smoke to adjacent plenum areas and potentially to more distant and widespread areas within a building. The cellular foamable fluoropolymer products of this disclosure can typically reduce the quantity of combustible materials by 30 to 60 percent based on the extent of the foaming process within insulations, fillers and jacket materials.
The products of the present disclosure have also been developed to support the possible adoption of a new NFPA standard referenced as NFPA 255 entitled “Limited Combustible Cables” with less than 50 as a maximum smoke index and NFPA 259 entitled “Heat of Combustion” which includes the use of an oxygen bomb calorimeter that allows for materials with less than 3500 BTU/lb. for incorporation into cabling systems and buildings wherein survivability of the communication network from fires is required i.e. (military installation such as the Pentagon in Washington D.C.).
For these applications requiring survivability from flame spread and smoke generation, the cellular products of the present disclosure will be an effective method for reducing material content and the fuel load of cables in such critical environments.
Table 2 provides a hierarchy of fire performance standards for North America and Europe.
TABLE 2Flammability Test Methods and Level of Severity for Wire and CableCable TypeTest MethodIgnition Source OutputDurationLimitedUL2424/NFPA8,141 KJ/kg(3,500 BTU/lb.)10 min.Combustible259/255/UL723CMPSteiner Tunnel88 kW(300 k BTU/hr.)20 min.UL 910/NFPA 262CMRRISER154 kW(527 k BTU/hr.)30 min.UL 1666/UL2424/NFPA 259CPDSingle Burning Item30 kW(102 k BTU/hr.)30 min.Class D(20 min burner)CPDModified IEC 60332-330 kW(102 k BTU/hr.)20 min.Class D(Backboard behind ladder(heat impact))CMIEC 60332-320.5 kW(70 k BTU/hr.)20 min.CMXVertical Tray20.5 kW(70 k BTU/hr.)20 min.CMUCIEC 60332-1/ULVW-1Bunsen Burner 1 min.(15 sec. Flame)Cable Fire Performance (Levels of Severity)NFPA 255 & NFPA 259/LC/CPD Class B1+/UL 2424(most stringent)NFPA 262/EN 50289/FT-6/CPD Class B1/UL 910|UL 1666 Riser/FT-4/CPD Class C & B2|UL 1581 Tray/IEC 60332-3/FT-2/CPD Class D|VW 1/IEC 60332-1/FT-1/CPD Class E(least stringent)